This Project, Project 3, Binaural Processing and Sound Source Determination, is a psychoacoustic study involving human listeners' use of spatial cues in sound source determination. The Project's focus is on stimulus conditions that involve locating more than one potential sound source. The Project continues work on the lateralization/localization of multiple spectral components using a newly developed two-dimensional stimulus classification procedure. This procedure estimates the relative weights listeners assign to various sound sources when they attempt to lateralize/localize one or more sources when all of the sound sources are presented at the same time. The cocktail party effect (the use of spatial cues in the ability to attend to one source when many sources are present) will be studied in a procedure that is similar to a real-work listening condition involving three or more concurrently presented sound sources. In many listening conditions the sound source and its echoes are all present when one attempts to locate the sources. A series of studies is planned to better understand how the auditory system processes echoes. These studies involve the Precedence effect, the Franssen effect, and the recently discovered Clifton effect. All of these effects indicate that spatial information concerning echoes is suppressed when a source and its echoes are localized. Recent results also suggest that a listener's immediate prior experience with a source and its echoes influences how echoes are processed. Studies are proposed to investigate these aspects of echo processing. Many stimuli can be generated which produce a 'dichotic pitch.' The generation of a dichotic pitch indicates that the binaural auditory system has used interaural differences to segregate one spectral region from another. Studies are planned investigating dichotic pitch stimuli as one means of understanding how interaural differences can be used to segregate one sound from another. Our proposed work, therefore, is based on a series of effects that appear to be related to the situation in which listeners are asked to determine the location of a sound source in the real world, especially considering that in the real work there is usually more than one sound source present. Thus, studies of binaural interference, the cocktail party effect, echo processing, and dichotic pitch all involve processing spatially separated sounds when more than sound source is present.